Switching component for detecting contact erosion

ABSTRACT

Switching components with contact parts that are mounted on a contact carrier in a switch housing may include devices for monitoring the contact erosion. The contact carrier may be split (sub-divided) and contact parts can be slotted at the rear and mounted on the sub-divided contact carrier. Thus, the oscillation response (vibration response) of the contact carrier in particular can be used as a measure of the erosion of the contact parts.

BACKGROUND OF THE INVENTION

The present invention relates to a switching component, and particularlyrelates to a safety switch or a power switch, with contact partsattached to a contact carrier, including a portion for detecting contacterosion.

In switching components, burning erosion occurs on the contact partswith each switching operation. Depending on the stress due to thecurrent or voltage, this erosion ultimately leads to failure of theswitching component. This is especially true when switchingshort-circuit currents in power switches, because the resulting arcscause an especially great erosion of the contact surfaces.

Erosion mainly limits the lifetime of a switch. Currently, the contactparts or even the entire switch must be routinely replaced after acertain lifetime, regardless of whether there has actually been anyconsiderable amount of erosion of the contact parts.

Several proposals in the state of the art have been made that wouldpermit monitoring of the erosion of contact parts, such as detectingcontact erosion using accessory electric, mechanical or X-ray equipment.For example, German patent (ALS) 2,405,149 discloses a switchingcomponent where the change in switch travel length due to contacterosion is detected. In order to achieve a reliable display of thecontact erosion, however, a relatively complicated mechanical design isnecessary.

In addition, German patent (OLS) 3,714,802 discloses an electric switchin which at least one of the contact parts is provided with an opticalfiber whose transmission properties can be measured externally by meansof suitable optical equipment. Due to an appropriate arrangement of theoptical fiber, excessive contact erosion leads to destruction of theoptical fiber and thus to a change in the optical transmissionproperties. However, introducing optical fibers into the contact partsto be applied to the contact carriers requires an additional productionstep. Therefore, such contact parts including incorporated opticalfibers are also expensive and difficult to handle as a part ofintegrated production of switching components.

SUMMARY OF THE INVENTION

The present invention relates to a switching component including otherdevices for monitoring the contact erosion. In the switch according tothe present invention, the end of the lifetime of the contact parts canbe predicted without interrupting the operation of the switch or havingto open the switch housing.

In the present invention, the contact carrier is split (sub-divided) andthe contact parts are slotted at the rear and are mounted on the splitcontact carrier. The contact carrier is preferably split asymmetricallyand the contact parts are preferably slotted asymmetrically at the rear.Both moving and fixed contact carriers can be used with the contactparts in this regard.

In the switching device according to the present invention, the contactcarriers that are joined together when the contact parts are new becomeseparated when contact erosion becomes great enough. The resultingchange in physical conditions can be detected easily. The detection maytake place on the basis of the oscillational behavior (vibrationalbehavior) of the contact bridge by mounting an oscillation sensor(vibration sensor) on the contact bridge or mounting a microphone in thehousing. As another example, the voltage between the two contactcarriers can be measured to provide a signal for contact erosion atleast during the switching operation.

In the present invention, it is especially advantageous that theprerequisites for detecting contact erosion may be created merely by aslight change in the design of the contact carrier and the respectivecontact parts. The sensors can be mounted inside the switch housing oron the outside of the switch housing.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional details and advantages of the present invention may bederived from the following description of embodiments of the inventionin conjunction with the attached drawings.

FIG. 1 illustrates a contact carrier with a traditional design.

FIG. 2 illustrates a type of contact carrier according to an embodimentof the present invention with the respective contact parts.

FIG. 3 and FIG. 4 illustrate two different possibilities for analysiswith a contact carrier according to FIG. 2.

FIG. 5 illustrates another possibility for analysis of the switchingcomponent according to FIG. 2.

DETAILED DESCRIPTION

Identical parts in the figures are provided with the same referencenumbers. FIGS. 1 to 3 and 5 are shown as perspective views and FIG. 4illustrates a side view. The figures are described together to someextent.

FIG. 1 illustrates a contact carrier 1 with a contact part 2 attached toeach end. Contact parts 2 together with contact carrier 1 may form amovable contact bridge that is mounted inside a switch housing in such away that contact is made by moving the contact bridge. Contact surface 3of contact parts 2 (in other words, the contact surface opposite contactcarrier 1) is brought in contact with mating contacts (not shown in FIG.1), which contact constitutes a switching operation.

With such electric switching operations, the contact materialnecessarily erodes due to the electric arcs and the contact parts wearaway. Since the actual wear on the contact parts cannot be detected fromoutside the switch housing and becomes apparent only when the switchfails completely, such contact parts or even complete switches arecurrently replaced after a certain period of operation. The allowedoperating times of switching components are usually assumed to be soshort that, even under intense loads, malfunctioning of the switch canbe practically ruled out during its service life.

According to FIG. 2, a contact carrier 10 is made of two parallelcarrier parts 11 and 12. The respective contact parts 20 are providedwith a slot 21 at the rear and are attached in a slotted condition oncarrier parts 11 and 12. When it is new, switch surface 23 of thecontact parts is designed like switch surface 3 of contact parts 2.

The physical conditions of contact carrier 10 change in accordance withthe erosion of contact parts 20. Specifically, the oscillation responseof contact carrier 10 with the two carrier parts 11 and 12 without anyerosion of contact parts 20 will be different from the oscillationresponse of contact carrier 10 with carrier parts 11 and 12 that areseparated due to erosion of contact parts 20. The oscillation responsein particular can be detected by means of an oscillation sensor on thecontact bridge, for example. As an alternative, a microphone 19 may bemounted in the switch housing, as shown in FIG. 5.

To amplify the difference in oscillation response when contact parts 20are new and when they are eroded, the gap in contact carrier 10 may alsobe positioned asymmetrically. The detection results are then lessambiguous because there are two different frequencies in the oscillationresponse when carrier parts 11 and 12 have different widths.

FIG. 2 illustrates the splitting (sub-division) of contact carrier 10into carrier parts 11 and 12 and the slotting of the respective contactparts on the movable contact. It is possible to apply the principle ofsub-division or slotting in a corresponding fashion to the fixedcontacts which are also mounted on suitably designed contact carriersand to design all contact parts so they are slotted. The detectionsensitivity may be improved in this way.

As an alternative to detection of the oscillation response, the voltagebetween the two parts 11 and 12 of contact carrier 10 in FIG. 2 can bemeasured, because when contact erosion has reached a sufficient extent,a measurable voltage signal occurs at least during the switchingoperation, and this signal can be analyzed.

FIG. 3 illustrates contact carrier 10 in a perspective view with thesplit carrier parts 11 and 12 and contact parts 20 according to FIG. 2in contact with fixed contact parts 30 on contact carriers 31 (onlypartially indicated) by means of which one phase of a line system, forexample, is switched. In this arrangement, the rear of carrier parts 11and 12 is short-circuited across a resistor 13 and a photodiode 16. Thephotodiode 16 is paired with a phototransistor 17 in the housing. Due tosuch a switching, the voltage signal generated between carrier parts 11and 12 when contact parts 20 are eroded can be delivered directly as anoptical signal as an indication that switch parts 20 are worn out.Accordingly, the voltage signal can be sent to an analyzer 18 by way ofthe potential-dividing optical coupler 15 formed by photodiode 16 andphototransistor 17.

FIG. 4 illustrates a side view of contact carrier 10 designed accordingto FIG. 2 with carrier parts 11 and 12 and contact parts 20, with therespective fixed contact parts 30 on contact carriers 31. The resultingswitch bridge is usually operated by an electromagnet 40 with armature42 and yoke 43 for the switching operation. Therefore, an operating rod41 is connected to armature 42 which is opposite to yoke 43 ofelectromagnet 40. Yoke 43 of electromagnet 40 has a coil 44 for electricoperation. It has been found that the oscillation of contact carrier 10is manifested as harmonic oscillations in the coil current of operatingmagnet 40. When the oscillation response of contact carrier 10 changesdue to the erosion of contact parts 20, ultimately resulting in twocarrier parts 11 and 12 oscillating separately, the frequencies of theharmonics in the coil current also change. These frequencies can bedetected by suitable filters 45.

No additional measurement devices are necessary for detecting theoscillation response of the contact carrier in FIG. 4 in particular.This further simplifies the design.

We claim:
 1. A switching component comprising:at least two contact partsmounted on a contact carrier in a switch housing; and means formonitoring contact erosion of the at least two contact parts, the meansfor monitoring being coupled to the contact carrier, wherein the contactcarrier is divided and the at least two contact parts are slotted at arear side thereof and are mounted on the divided contact carrier.
 2. Aswitching component according to claim 1, wherein the switchingcomponent is used on a moving contact carrier and respective contactparts.
 3. A switching component according to claim 1, wherein theswitching component is used on a fixed contact carrier and respectivecontact parts.
 4. A switching component according to claim 1, whereinthe means for monitoring detects an oscillation response of the contactcarrier during the switching operation.
 5. A switching componentaccording to claim 4, wherein the means for monitoring includes anoscillation sensor mounted on the contact carrier.
 6. A switchingcomponent according to claim 4, wherein the means for monitoringincludes a microphone mounted on the switch housing.
 7. A switchingcomponent according to claim 1, wherein the means for monitoringincludes means for measuring and displaying an electric voltage betweenthe two divided contact carriers.
 8. A switching component according toclaim 7, further comprising a photodiode displaying the contact erosion.9. A switching component according to claim 8, further comprising:aphototransistor connected downstream from the photodiode, wherein thephotodiode serves as an optical coupler for potential division of themeasurement voltage supplied to an analyzer when the contact parts areeroded.
 10. A switching component according to claim 1, furthercomprising:an electromagnet initiating the switching operation, andmeans for detecting harmonics manifested in the coil current of theelectromagnet, wherein the harmonics are a signal relating to theoscillation state of the contact carrier.
 11. A switching componentaccording to claim 10, further comprising:at least one filter fordetecting the harmonics manifested in the coil current of theelectromagnet.
 12. A switching component according to claim 1, whereinsaid switching component comprises a safety switch.
 13. A switchingcomponent according to claim 1, wherein said switching componentcomprises a power switch.
 14. A switching component according to claim1, wherein the contact carrier is asymmetrically divided and the atleast two contact parts are asymmetrically slotted at the rear side. 15.A switching component according to claim 14, wherein the switchingcomponent is used on a moving contact carrier and respective contactparts.
 16. A switching component according to claim 14, wherein theswitching component is used on a fixed contact carrier and respectivecontact parts.
 17. A switching component according to claim 14, whereinthe means for monitoring detects an oscillation response of the contactcarrier during the switching operation.
 18. A switching componentaccording to claim 17, wherein the means for monitoring includes anoscillation sensor mounted on the contact carrier.
 19. A switchingcomponent according to claim 17, wherein the means for monitoringincludes a microphone mounted on the switch housing.
 20. A switchingcomponent according to claim 14, wherein the means for monitoringincludes means for measuring and displaying an electric voltage betweenthe two divided contact carriers.
 21. A switching component according toclaim 20, further comprising a photodiode displaying the contacterosion.
 22. A switching component according to claim 21, furthercomprising:a phototransistor connected downstream from the photodiode,wherein the photodiode serves as an optical coupler for potentialdivision of the measurement voltage supplied to an analyzer when thecontact parts are eroded.
 23. A switching component according to claim14, further comprising:an electromagnet initiating the switchingoperation; and means for detecting harmonics manifested in the coilcurrent of the electromagnet, wherein the harmonics are a signalrelating to the oscillation of the contact carrier.
 24. A switchingcomponent according to claim 23, further comprising:at least one filterfor detecting the harmonics manifested in the coil current of theelectromagnet.